Method of shaping a crystal by acid cutting



Oct. 1, 1968 D. J. SHANEFIELD ETAL 3,404,049

METHOD OF SHAPING A CRYSTAL BY ACID CUTTING Filed March 12, 1965INVENTORS. DANIEL J. SHANEF/ELO EMER Y Mcunmak ATTNEY United StatesPatent ABSTRACT OF THE DISCLOSURE This is a method of shaping a solidcrystal object. A container is filled with an acid which is capable ofetching the crystal object. A U-shaped tube is placed in the containerand one end is immersed in the acid. An inert liquid which is heavierthan the acid is poured into the other end of the tube creating aninterface between the two liquids at the immersed end of the tube. Theobject is submerged a predetermined distance into the immersed end ofthe tube so that the crystal can be cut at the interface between the twoliquids.

This invention relates to a device for cutting metallic crystals andmore particularly to a device for the chemical cutting of crystals.

Devices for cutting crystals without introducing dislocations areordinarily rather complex especially if flat surfaces are desired andeven the simplified versions known to the art have been difficult toadjust and operate. One such device is the electrolytic cutter whereinthe crystal is immersed in a receptacle containing an electrolyte whichis disposed between two insulating liquid layers, the insulating layersand the electrolyte being immiscible and the bottom insulating layerbeing heavier than the electrolyte. The crystal sample to be cut formsan anode and an annular cathode surrounds the crystal at the interfaceof the electrolyte and the top insulating layer. The anode and thecathode are then connected to a source of current and during theelectrolytic action that takes place, the metal is displaced and forms aviscous layer which is heavier than the electrolyte. However, thedisadvantage of this method is that the viscous layer which is the saltformed by the reaction of the electrolyte with the crystal, tends toaccumulate within the electrolyte and in time converts the acid phase toan inert phase thus interfering with the cutting operation.

Another method of cutting crystals is the spark erosion method which ispurely electrical without the use of chemical materials.

Still another method is the purely chemical method using a wet stringcrystal cutter wherein the thread or string is disposed around thecrystal to be cut at the place where the cut is to be made and acid iswicked up through the thread, and the chemical reaction between the acidand the crystal with constant tension on the string results in thecutting of the crystal. However, the difiiculty of this method is thatit is diflicult, even impossible, to maintain the string in a straightpath so that a wavy and irregular cut generally results.

An object of this invention is to provide a device for purely chemicalcutting of crystals without string thereon and wherein the cut isgenerally straight and regular within close tolerances.

A feature of this invention is a method of shaping a solid objectcomprising immersing the solid object in a corrosive liquid capable ofchemically reacting with said solid object, and surrounding the immersedmetallic object with an inert fluid leaving a portion of the solidobject in contact with the corrosive liquid. The solid object can be acrystal, such as quartz or metal, or any other 3,404,049 Patented Oct.1, 1968 material which can be cut by this method. The corrosive liquidmay be an acid or any liquid substance that will react with the solidobject immersed therein.

The above-mentioned and other features and objects of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the sole figure of this invention.

With'reference to the figure, there is shown a container 1 which hastherein an'acid 2 capable of reacting with a metal sample or crystal 3which is suspended within the acid 2 by means not shown. A U-shaped tube4 is immersed in the acid 2 with the end 5 thereof surrounding theimmersed portion 6 of the crystal 3. There is thus left a portion 7 ofthe crystal 3 exposed to the action of the acid 2. An inert liquid 8,which is heavier than the acid 2, is poured into the U-tube 4 until itreaches the level 9 at the other end 5 of the U-tube. A buffer material10 which may be glass wool, is disposed within the U-tube 4 directlybelow the end portion 6 of the crystal 3 so that when the crystal is cutthrough at the area 7 and the cut off piece 6 falls, it will firststrike the glass wool 10 and not be injured by the wall of the U-tube.

If we consider a metallic sample 3 to be a copper crystal which is to becut, then the acid 2 would consist of two parts concentrated nitric acidplus three parts water. The inert fluid 8 could be 20 parts oftetrachloroethylene and one part of linoleic acid. In the case of coppercrystals, it was found that a large amount of acid phase was necessary(300 ml.) for a /2 inch diameter crystal. If less acid is used, the acidphase gets too dense as copper nitrate accumulates resulting eventuallyin an inversion of the two phases. By restricting the inert phase to asmall container, such as the U-tu'be 4, most of the space within thecontainer 1 can be occupied by acid. Another advantage of the U-tube isthat the heavy copper nitrate solution as it is formed can flow over thelip of the narrow U-tube at the end 5 and down into the bottom of thecontainer 1, thus removing the spent acid from the cutting region. Thisinsures that the acid phase and the inert phase is not intermixed. Also,the hydrostatic force exerted by the inert liquid 8 allows for easycorrection of the meniscus level and maintains an upward pressure on themeniscus thus insuring that the copper nitrate formed will not penetrateinto the inert liquid but will spill over on the side of the U-tube intothe bottom of the container. This then provides for greater and moreaccurate control of the cutting process. The height of the meniscus canbe adjusted by adjusting the level of the heavy inert liquid in theU-tube, the inert liquid being heavier than the acid. Another advantageof this device is the adjustability of the surface tension of the inertliquid at the interface with an acid and the crystal by the use oflinoleic acid. This is effected by the linoleic acid causing the inertliquid to wet the copper surface and thus prevents the meniscus fromextending lower than the level shown in the figure. Furthermore,narrowness of the meniscus due to the 'small diameter of the U-tubeallows the copper nitrate to spill over more readily. Any inert fluidcan be used which is inert and heavier than the cutting fluid or acidand any acid can be used which is suitable for cutting.

The cutting fiuid can be any corrosive liquid which will react with theimmersed object to be shaped, such as an acid. The object may be anysolid, such as metallic or quartz crystals, which will react with thecutting fluid.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. A method of shaping a solid crystal object from a group consisting ofcopper and quartz in a container comprising the steps of:

filling 'said container with a liquid acid, said acid being capable ofetching said crystal object;

placing a U-shaped tube in said container, one end of said tube beingimmersed in said acid;

pouring an inert liquid into the other end of said tube,

said inert liquid being heavier than said acid whereby an interface iscreated between said two liquids in the immersed end of said tube;

submerging said object into the immersed end of said tube to apredetermined distance;

and cutting said crystal in said interface between said two liquids. 2.A method of shaping a solid crystal object according to claim 1 whereinsaid acid is of two parts concentrated nitric acid and three partswater.

3. A method of shaping a solid crystal object according to claim 1wherein said inert liquid is of 20 parts tetrachloroethylene and 1 partlinoleic acid.

References Cited UNITED STATES PATENTS 2,952,528 9/1960 Corneilson156-17 JACOB H. STEINBERG, Primary Examiner.

